1. Field of the Invention
The present invention relates to a water-activated cell having excellent storability and a method of power generation using the same.
2. Description of the Related Art
A cell is a device that converts chemical energy of a substance directly into electric energy. Cells can be classified into primary cells that discharge electric power until their chemical energy is used up, secondary cells capable of being reused by storing chemical energy again by a charging operation after being used up, and fuel cells that obtain electric energy by continually being supplied with a substance having chemical energy from outside. Currently, numerous types of cells have been developed. Each cell has different advantages and disadvantages with respect to each item of environmental safety, economy, amount of electric energy that can be supplied, portability, storage and preservation properties, adaptation to an environment of use, recyclability, and the like, so that cells are selected and put to practical use in accordance with an intended use. Critical technical factors that are common to all cells are what chemical substances are used for reaction, how the reaction is initiated, and in what form the chemical substances are stored.
A cell makes use of two kinds of chemical substances, namely, a reducing agent that causes a reduction reaction (giving electrons to the opposing party or drawing oxygen therefrom) and an oxidizing agent that causes an oxidation reaction (drawing electrons from the opposing party or giving oxygen thereto). By causing these reactions separately at two electrodes that oppose each other, the energy of generated electrons is discharged to the outside (ions produced at the two electrodes accompanying the generation of electrons are neutralized within the cell). Reaction efficiency depends on the kind of the chemical substances to be used, electrode activity, and the condition of reaction fields including electrolytes. Especially, what substances are to be selected to constitute a cell is a point affecting whether the whole cell system will be good or bad not only at the time of use but also at the time of storage and at the time of discarding after use.
For example, in conventional cells such as zinc-manganese system or mercury system primary cells, nickel cadmium secondary cells, nickel hydrogen secondary cells, lithium ion secondary cells, and lead storage cells, the active substances thereof are made of metal. These metallic active substances include lithium which is a flammable dangerous substance, mercury, cadmium, and lead which are substances harmful to the environment, nickel and cobalt which are rare substances that are depletable resources, zinc which is accompanied by high recycling costs, and the like. For these reasons, existing cells involve numerous problems such as the danger of leakage of dangerous substances and environmentally harmful substances, fear of depletion of rare resources, and high costs at the time of recycling.
In addition, since these cells hold liquid electrolytes therein, their active material decrease in amount due to a self-discharging reaction even in a stored state with no outside load imposed. For this reason, existing cells do not have sufficient storability. On the other hand, a sea water cell is commercially available as a cell with enhanced storability. This cell is a primary cell in which silver chloride or lead chloride is used as the positive electrode, and magnesium is used as the negative electrode. The sea water cell is stored in a state without containing an electrolyte solution, and starts to discharge electricity by being immersed in sea water or pure water. This sea water cell can be used as a power source for marine life-saving lamp, a power source for ignition of a detonator, a power source for marine observation equipment, a power source for starting marine-use equipment, a power source for small toys, an emergency power source, or the like purpose (see the Yuasa Corporation website at www.yuasa-jpn.co.jp/seihin/special/kaisui.html). However, since its active material is a metal, there are problems similar to those of the aforementioned primary cells and secondary cells, and a solution to these problems is desired.
Therefore, cell technology providing high storability is earnestly desired. At the same time, a cell technology with less effect on the environment is earnestly desired.